Conventionally, in production of an organic EL element, a vapor deposition mask that is composed of a metal formed by a number of microscopic slits being arranged in parallel with one another at microscopic spaces in a region that should be subjected to vapor deposition, for example, has been used in formation of an organic layer or a cathode electrode of an organic EL element. While in the case of using the vapor deposition mask, the vapor deposition mask is placed on a substrate front surface that should be subjected to vapor deposition and is held by using a magnet from a back surface, the rigidity of the slits is extremely small, and therefore, distortion easily occurs to the slits when the vapor deposition mask is held on the substrate front surface, which becomes an obstacle to enhancement in definition or upsizing of the products in which the slit lengths are large.
Various studies have been made on the vapor deposition masks for preventing distortion of slits, and, for example, Patent Literature 1 proposes a vapor deposition mask including a base plate that also serves a first metal mask including a plurality of openings, a second metal mask including a number of microscopic slits in regions to cover the aforementioned openings, and a mask pulling and holding device that positions the second metal mask on the base plate in a state of being pulled in the longitudinal direction of the slits. Namely, the vapor deposition mask with two kinds of metal masks being combined is proposed. It is indicated that according to the vapor deposition mask, slit precision can be ensured without occurrence of distortion to the slits.
Incidentally, in recent years, with upsizing of the products using organic EL elements or increase in substrate sizes, a demand for upsizing is also growing with respect to vapor deposition masks, and the metal plates for use in production of the vapor deposition masks composed of metals are also upsized. However, with the present metal processing technique, it is difficult to form slits in a large metal plate with high precision, and even if distortion in slit portions can be prevented by the method proposed in the above-described Patent Literature 1 or the like, these cannot respond to enhancement in definition of the slits. Further, in the case of use of a vapor deposition mask composed of only a metal, the weight thereof also increases with upsizing, and the total mass including a frame also increases, which becomes a hindrance to handling.
In the vapor deposition mask proposed above, in order to reduce the weight of the vapor deposition mask, it is needed that the thickness of the vapor deposition mask composed of a metal be made small. However, in the case where the thickness of the vapor deposition mask composed of a metal is made small, the strength of the vapor deposition mask decreases by that amount, and there arise the new problems that the vapor deposition mask suffers deformation and that handling becomes difficult.